An animated plotting method in which the states of cutting workpieces by means of a plurality of tool rests of a lathe are simulatively displayed on a single screen at the same time is a known technique. According to the conventional animated plotting method, a plurality of spaces obtained by splitting a monitoring screen depending on the number of the tool rests are assigned to the plottable ranges of the tool rests, or alternatively, the entire monitoring screen is fixedly assigned as the integral plottable range of all of the tool rests.
FIG. 5 illustrates, by way of example, a conventional animated plotting with the monitoring screen split into two display spaces correspondingly to a couple of tool rests. As seen from the figure, a display screen 101 of a display means 100 such as a CRT display unit includes a halved screen consisting of a first plottable range 101a for a tool 104 mounted on a first tool rest for exclusively machining a workpiece 103 loaded on a first main spindle 102, and a second plottable range 101b for a tool 107 mounted on a second tool rest for exclusively machining workpiece 106 mounted on a second main spindle 105, whereby the states of cutting the workpieces 103 and 106 each mounted on corresponding main spindles can be simulatively plotted on the same screen. In this case, the boundary 108 between the two plottable ranges cannot be shifted on the screen 101.
Moreover, the screen 101 is not necessarily allowed to correctly represent a mutual positional relationship between the first main spindle 102 and the second main spindle 105. Hence, if either the tool 104 or the tool 107 of the tool rests has moved beyond its plottable range, and such movement is plotted, the relative positions of the tool and the workpiece lying in the other plotting range may become inconsistent with each other to cause the problem of contradictory display.
Therefore, when a tool has moved to another range beyond its plotting range, normally, the plotting of such tool (in other range) will not be executed. In other words, the plotting of each tool rest will be clipped based on the corresponding plottable range.
FIGS. 7(a) and 7(b) are conceptual diagrams illustrating a function of the clipping processing. If the tool 104, mounted on the first tool rest, lies within its plottable range 101a, then the whole image of the tool 104 can be plotted as shown in FIG. 7(a). If the part of the tool 104 lies beyond the boundary 108, however, such part of the tool 104 lying beyond the plottable range 101a will automatically be clipped as shown in FIG. 7B. Accordingly, even when the tool 104 of the first tool rest has moved into the machining area of the second tool rest, the configuration of the tool 104 and the cutting process will not be displayed. Similarly, even if the tool 107 mounted on the second tool rest has moved into the machining area of the first tool rest, the tool 107 and its cutting process will not be displayed.
Also, in the case of the conventional example shown in FIG. 6, the workpiece 103 loaded on the first main spindle 102, the tool 104 mounted on the first tool rest for cutting the workpiece 103, the workpiece 106 loaded on the second main spindle 105 and the tool 107 mounted on the second tool rest for machining the workpiece 106 are integrally displayed in the same screen 101 while maintaining their relative positional relationships with one another. For example, according to this simulative plotting, the movement of the tool 104 mounted on the first tool rest from the current position of the workpiece 103 to the side of the workpiece 106 can be sequentially plotted. As apparent from this figure, however, the sizes of the images of the workpieces 103 and 106 and the tools 104 and 107 have to be reduced inevitably, and thus it is difficult to have a clear plotting of the machining state displayed on the screen.
Since the conventional NC apparatus for a multi-system lathe was exclusively intended to perform a cutting operation for each of the main spindles by providing a plurality of tool rests corresponding to the main spindles, or intended to cut a workpiece loaded on a single main spindle by means of a plurality of tool rests, the conventional animated plotting method described above and shown in FIG. 5 is good enough for the execution of a full simulation by the conventional animated plotting method.
However, the recent NC apparatus for a multi-system lathe is often applied even to such a case where the tool 104 mounted on the first tool rest is moved to the machining area assigned to the second tool rest for cutting the workpiece 108 loaded on the second main spindle 105 as shown in FIG. 8(a), or such a case where the workpiece 103 loaded on the first main spindle 102 is subjected to the cutting operation by both the tool 107 of the second tool rest and the tool 104 of the first tool rest as shown in FIG. 8(b). In the cases of such application, therefore, it is difficult to simulatively plot such cutting operation by using the animated plotting method as such shown in FIG. 5. On the other hand, the display method shown in FIG. 6, which does not use the split screen, has a disadvantage in that it is not suited for displaying the cutting conditions, that is, the relationship between the tools and the workpieces as good as necessary as discussed previously.